Ruminant animals, including cattle, sheep, giraffe, deer, goats, bison and camels, and more particularly cattle and sheep, comprise an important group of animals that require periodic administration of medicines, nutrients and other biologically active agents (which are hereinafter referred to in their broadest sense as "drugs") for the treatment and alleviation of various conditions and for better health.
Ruminants have a complex three or four compartment stomach, with the rumen being the largest compartment. The rumen serves as an important location for receiving and absorbing medicines and nutrients into other compartments including the abomasum and the intestine.
There are numerous ruminal delivery devices known in the art which are capable of prolongedly releasing drugs. These devices are easily swallowed by the ruminant or otherwise introduced into the rumen and remain within the rumen for a long period of time without being regurgitated or otherwise expelled. Typical devices having an osmotic portion which imbibes ruminal fluid and expands, forcing a liquid or paste drug portion of the device through an orifice into the rumen, are those disclosed in U.S. Pat. Nos. 4,595,583 and 4,612,186, the disclosures of which are incorporated herein by reference.
In order to insure that these devices remain in the rumen for a prolonged period of time, a density element is often incorporated into the device. Typically, the density element is manufactured from a material such as iron or steel, iron shot, iron shot coated with iron oxide, magnesium alloy, copper oxide or mixtures of cobalt oxide and iron powder, and the like. Such density elements typically have sufficient density to bring the overall density of the delivery device to a level greater than the density of ruminal fluid (approximately 1 gm/mL) and preferably to an overall density of at least 2 gm/mL.
The osmotic ruminal delivery device or bolus has encountered some difficulties, however; the daily output of the bolus has been seen to often be highly erratic. It has been found that density elements made from materials such as iron, magnesium or zinc are susceptible to corrosion in water or ruminal fluids. This corrosion causes production of gases, which gases enter into other portions of the device and accumulate as gas bubbles which can cause fissures within the drug formulation and/or the osmotic expandable member. The presence of such fissures can cause gaps in the flow of drug formulation or a rapid expulsion of a portion of the lo formulation. Typically, the formation of a fissure causes a rapid expulsion of a portion of the formulation (fissure/bubble formation) followed by gaps or a decrease in the flow of drug formulation (fissure closure or expulsion through orifice). Thus, erratic flow is observed with days of low output and days of high output. In one effort to decrease corrosion, density elements of sintered metal have been impregnated during manufacture with an inert hydrophobic material such as silicone oil, mineral oil or wax (see, U.S. Pat. No. 5,206,024 and PCT patent publn. WO 90/11856). This method, while apparently successful, has the disadvantages of being a time-consuming process during, and adding considerable expense to, the manufacture of the ruminal delivery device. Additionally, this is not a practical solution when the density element is not of the fragmentable sintered type disclosed in the above publications.